PROJECT SUMMARY/ABSTRACT . Bladder cancer is a leading cause of death in the US and the most expensive cancer to treat. Despite this, there has been only one new bladder cancer therapy, the checkpoint inhibitor atezoluzimab, approved in the past 30 years. Oncolytic viruses, viruses that selectively infect and kill cancer cells, are a potent new class of immunotherapy that mediate anticancer activity by direct virus induced killing and robust activation of immune responses against tumor associated antigens. Vyriad's lead oncolytic measles virus product, MV-NIS, has shown clinical safety and efficacy following intravenous and intraperitoneal treatment in patients with advanced multiple myeloma and ovarian cancer respectively and potently kills bladder cancer cell lines in in vitro studies. Our goal is to develop oncolytic MV-NIS as a new treatment for bladder cancer, a malignancy that has demonstrated susceptibility to immunotherapy. A majority of patients are diagnosed with non-muscle invasive disease (NMIBC), of which approximately 50% of patients fail first line therapy. These patients, and patients with muscle invasive disease (MIBC), have no effective therapeutic options and facing the likelihood of disease progression or metastasis,often undergo radical cystectomy (complete bladder removal) which significantly impacts quality of life. In this SBIR fast-track application we propose to (I) confirm feasibility and identify optimal conditions for intravesical administration of MV-NIS and (II) carry out a Phase 1 clinical trial to evaluate intravesical MV-NIS therapy in patients scheduled to undergo radical cystectomy. This study will provide the critical demonstration of feasibility and safety of intravesical MV-NIS administration, as well preliminary indication of therapeutic efficacy to inform the decision to advance MV-NIS therapy in a pivotal clinical trial to seek approval as a novel bladder cancer therapy. We utilize an innovative clinical trial design that allows correlative analysis to define mechanism of action of MV-NIS therapy including characterization of antitumor immune responses. This will inform future studies to combine MV-NIS therapy with approved checkpoint inhibitors to potentially develop a more potent therapeutic approach for patients with locally advanced or metastatic bladder cancer. We are bringing together Vyriad's team, leading experts in oncolytic virotherapy development, with Mayo Clinic's nationally number one ranked Urology department, to perform this study that will, if successful, lead to the approval of a new, much-needed treatment for bladder cancer patients.